The problems posed by substances which delete the atmospheric ozone layer (ODP: ozone depletion potential) were addressed in Montreal, where the protocol imposing a reduction in the production and use of chlorofluorocarbons (CFCs) was signed. This protocol has been the subject of amendments which have required that CFCs be withdrawn and have extended regulatory control to other products, including hydrochlorofluorocarbons (HCFCs).
The refrigeration and air-conditioning industry has invested a great deal in the replacement of these refrigerants, and as a result, hydrofluorocarbons (HFCs) have been marketed.
The (hydro)chlorofluorocarbons used as expansion agents or solvents have also been replaced with HFCs.
In the automotive industry, the air-conditioning systems for vehicles sold in many countries have changed from a chlorofluorocarbon (CFC-12) refrigerant to a hydrofluorocarbon (1,1,1,2-tetrafluoroethane: HFC-134a) refrigerant which is less harmful to the ozone layer. However, from the viewpoint of the objectives set by the Kyoto protocol, HFC-134a (GWP=1300) is considered to have a high warming potential. The contribution to the greenhouse effect of a fluid is quantified by a criterion, the GWP (global warming potential) which indexes the warming potential by taking a reference value of 1 for carbon dioxide.
Since carbon dioxide is non-toxic and non-flammable and has a very low GWP, it has been proposed as a refrigerant in air-conditioning systems as a replacement for HFC-134a. However, the use of carbon dioxide has several drawbacks, in particular linked to the very high pressure at which it is used as a refrigerant in the existing apparatuses and technologies.
Document WO 2004/037913 discloses the use of compositions comprising at least one fluoroalkene having three or four carbon atoms, in particular pentafluoropropene and tetrafluoropropene, preferably having a GWP at most of 150, as heat-transfer fluids.
Document WO 2005/105947 teaches the addition to tetrafluoropropene, preferably 1,3,3,3-tetrafluoropropene, of a blowing coagent such as difluoromethane, pentafluoroethane, tetrafluoroethane, difluoroethane, heptafluoropropane, hexafluoropropane, pentafluoropropane, pentafluorobutane, water and carbon dioxide.
Document WO 2006/094303 discloses binary compositions of 2,3,3,3-tetrafluoropropene (HFO-1234yf) with difluoromethane (HFC-32), and of 2,3,3,3-tetrafluoropropene with 1,1,1,2-tetrafluoroethane (HFC-134a).
Quaternary mixtures comprising 1,1,1,2,3-pentafluoropropene (HFO-1225ye) in combination with difluoromethane, 2,3,3,3-tetrafluoropropene and HFC-134a were disclosed in this document. However, 1,1,1,2,3-pentafluoropropene is toxic.
Quaternary mixtures comprising 2,3,3,3-tetrafluoropropene in combination with iodotrifluoromethane (CF3I), HFC-32 and HFC-134a have also been disclosed in document WO 2006/094303. However, CF3I has a non-zero ODP and poses stability and corrosion problems.
A heat exchanger is a device for transferring thermal energy from one fluid to another, without mixing them. The heat flux crosses the exchange surface which separates the fluids. Most commonly, this method is used to cool or heat a liquid or a gas that it is impossible to cool or heat directly.
In compression systems, the heat exchange between the refrigerant and the heat sources takes place by means of heat-transfer fluids. These heat-transfer fluids are in the gaseous state (the air in air-conditioning and direct expansion refrigeration), liquid state (the water in domestic heat pumps, glycolated water) or two-phase state.
There are various modes of transfer:                the two fluids are arranged in parallel and travel in the same direction: co-flow (antimethodic) mode;        the two fluids are arranged in parallel but travel in the opposite direction: counterflow (methodic) mode;        the two fluids are positioned perpendicularly: cross-flow mode. The cross-flow may be with co-flow or counterflow tendency;        one of the two fluids makes a U-turn in a wider pipe, which the second fluid passes through. This configuration is comparable to a co-flow exchanger over half the length, and for the other half, to a counterflow exchanger: pinhead mode.        